1. Field of the Invention
This invention in general relates to sonar apparatus, and particularly to an acoustic depth sounder.
2. Description of the Prior Art
A problem common to coastal and inland shipping channels is a question of whether or not the channel is deep enough and whether it is navigable with respect to obstructions protruding from the bottom.
The present technique for determining if the channel is deep enough is to make repeated parallel passes using a depth finder or sounder. In general, it is impractical to make enough parallel passes close enough together to make sure nothing protrudes above the desired depth. A technique commonly used to check for obstructions protruding from the bottom is to suspend a horizontal chain between two vessels at the depth to be checked. The two vessels then proceed down the channel with the chain snagging anything that protrudes above the depth being checked.
A broad beam angle would increase the area covered however, the depth resolution would be reduced. Increased resolution and coverage can be obtained with a multi-beam system wherein a plurality of adjacent beams are formed for each acoustic transmission. However, such a sophisticated system would be relatively expensive and would require specially designed displays.